LiCoO.sub.2 (lithium cobaltate) is now being widely used as an active material of a positive electrode of a secondary battery. LiCoO.sub.2 is being produced by a complicated and inefficient process comprising performing dry or wet mixing of powdery Li.sub.2 CO.sub.3 and powdery COCO.sub.3, preliminarily firing the mixture, carrying out pulverization and mixing of the preliminarily fired mixture and finally firing the resultant mixture as described in Japanese Patent Application Laid-Open Specification No. 294373/1989. In this process, not only is producing a LiCoO.sub.2 having a uniform composition difficult but also impurities are liable to occur as by-products, so that there has been a limitation in obtaining an active material having high charge and discharge characteristics. Moreover, cobalt output is small from the viewpoint of natural resources, and it is believed that meeting an increased demand would be difficult in the future.
In such circumstances, in place of the above COCO.sub.3, it has been attempted in recent years to treat NiCO.sub.3 or MnCO.sub.3 which is less expensive and more abundant in reserves, by the above method in order to use the same as an active material of a secondary battery. However, the LiNiO.sub.2 and LiMn.sub.2 O.sub.4 thus produced more clearly have the problems described above with respect to LiCoO.sub.2, with the result that the resultant products are so poor in purity that there is none which can be put into practical use.
On the other hand, Dyer et al developed another process for synthesizing LiNiO.sub.2, which was disclosed in Journal of American Chemical Society 76, 1499 (1954). This synthetic process is illustrated in FIG. 4, in which use is made of a double-pipe apparatus comprising an outer nickel pipe 1 and, inserted therein, an inner nickel pipe 2. The inner pie 2 has its inserted tip portion opened to thereby have a blowoff aperture 3. A predetermined amount, e.g., 50 g, of powdery LiOH 4 is filled in the outer pipe 1. While the overall double-pipe apparatus is heated at about 800.degree. C. to thereby melt the LiOH, oxygen is fed into the inner pipe 2 and blown out from the blowoff aperture 3 for 24 hours. Thus, LiNiO.sub.2 mass 5 covered with a LiOH film is formed on the inner surface of the outer pipe 1 at its portion near the blowoff aperture 3. This LiNiO.sub.2 mass 5 is washed with alcohol, and contaminant nickel oxide is removed by magnet attraction, thereby producing highly purified LiNiO.sub.2.
Although the process of Dyer et al is applicable in an experimental stage, it is not suitable for a mass-production and cannot be put into commercial use. Not only are a large amount of impurities formed as by-products, but also an apparatus having a complicated structure and an intricate processing are required, so that this process has not been put into practical use. Moreover, X-ray diffractometry shows that the LiNiO.sub.2 obtained by this process has a ratio of absorption peak intensity relating to crystal face (003) to absorption peak intensity relating to crystal face (104) of 100/95 =about 1.05, the above crystal face being defined by Miller indices (hkl). In general, when LiNiO.sub.2 is used as an active material of a positive electrode of a secondary battery, it has been found that the greater the above ratio of peak intensity of crystal face (003) to that of crystal face (104), the more excellent the charge-discharge characteristics thereof. At the above peak ratio, improvement of the charge-discharge characteristics can be expected only to a certain level.
The present invention has been made in view of these circumstances. An object of the present invention is to provide a process for producing a compound of the formula LiM.sup.3+ O.sub.2 (wherein M.sup.3+ is Ni.sup.3+ or/and Co.sup.3+) or LiMn.sub.2 O.sub.4 not only having a high purity, a high crystallization degree and a wide range of crystalline particle sizes but also exhibiting excellent charge-discharge characteristics when used as an active material of a positive electrode of a secondary battery, which process can be easily performed by simple operations, such as firing made at low temperatures for a short time, and which process permits industrial mass-production. Another object of the present invention is to provide LiNi.sup.3+ O.sub.2 for use in a positive electrode of a secondary battery obtained by the above process.